1. Field of the Invention
The present invention pertains to a digestion vessel, and more particularly, pertains to a microwave digestion vessel for use in a microwave oven including a valve assembly for venting high pressure.
2. Description of the Prior Art
Before the advent of microwave heating and microwave ovens, considerable time was required to dissolve a sample or samples for chemical analysis. This was especially so for elemental trace analysis, such as in the oil industry, the mining industry, and other related areas, including medical laboratories. Digestions were performed in open vessels on hot plates, or with other heating devices, resulting in long and extended digestion times, in addition to the exposure of personnel to caustic and harmful exhaust fumes from boiling acids or other digestion subjects.
With the advent of microwave heating and microwave ovens, elemental trace analysis became ever more so common, especially in utilizing a microwave digestion vessel in element trace analysis and the chemical procedures. The prior art problem with utilization of digestion vessels was that there was a certain amount of guess work required in the microwave heating techniques, especially pertaining to temperature, pressure, and time for a digestion procedure. During microwave heating it was possible, at elevated temperatures, to cause digestion vessels to expand considerably beyond normal size.
With the advent of Teflon PFA molded vessels, the Teflon PFA material provided a microwave digestion vessel which would function at elevated pressures and temperatures over time. Irrespective, there was still the necessity in the art for providing for the venting of high pressures and collection of vapors or gases in a slow controlled manner during microwave digestions.
Early attempts provided digestion vessels with valving assemblies with springs of ferrous or non-ferrous alloys in a valving arrangement, but this proved to be difficult as such a metallic assembly in a microwave oven cavity may cause arcing between adjacent metallic members, and required special shielding and time consuming periodic cleaning off of surface oxidation for proper non-impeded spring operation. These springs would also react with digestion vapors and gases offering potential contamination of the digestion container and contents thereof. These springs also deteriorated due to chemical reactions with digestion vapors, thus breaking down the spring qualities causing the springs to fail or relieve at a pressure other than desired allowing vessel vapors and contents to be expelled overboard at an inopportune time.
The present invention overcomes the disadvantages of the prior art by providing a microwave digestion vessel including a valve assembly for exhausting pressure in the digestion vessel on actuation of the valve assembly.